The work is a continuation of earlier studies on the stability of proteins and the factors that affect their unfolding and refolding reactions. Central to the studies is the use of mutants of the protein T4 lysozyme that permit us to assay the effects of individual amino acids on the equilibrium and rates of the folding reaction. We also perform variations of temperature, pH, ionic strength, and the concentration of denaturants and other substances so that we can develop complete thermodynamic and kinetic models. Our program is directed toward four aspects of this problem: 1. The study of low temperature unfolding. We have completed a study on one mutant, C3T54, and wish to look at the effects of mutations on the stability and kinetics of the unfolding and refolding reaction. 2. Studies of the interaction of proteins with water and denaturing agents. 3. Studies of the limited proteolysis of temperature-sensitive and other mutants in order to evaluate the local instabilities produced by mutations. 4. The continuation of our collaboration on families of mutants that have been generated in the laboratories of B. Matthews and F. Dahlquist. Their groups do the structural, dynamic and genetic studies while we specialize in thermodynamics, spectroscopy and kinetics.